The development of coastal lagoons for practical purposes is an old field. Its start was in China and India where, thousands of years ago, canals were built with primitive tools to serve navigation between lagoons. The lagoons were developed for fisheries and salt extraction by dams and gates regulating water tables and flow. The development of lagoons for engineering purposes accelerated after engineering tools became available for major engineering works involving management of water tables, dredging of canals and basins, establishment of fishing and later pleasure craft harbors and fish farms. With man's increased activities followed the possibility of certain adverse effects on the natural environment. This chapter deals with all of these subjects. In conclusion, I recommend proper planning, considering all pertinent environmental aspects associated with engineering in coastal lagoons.